蓖麻蒴果力学特性试验及仿真研究

Experimental and Finite Element Analysis of Mechanical Properties of Castor Fruit

为探究蓖麻蒴果破壳力变化规律及破裂机理,以1987品种、通蓖7号、通蓖9号及通蓖11号为研究对象,首先计算其球度,并采用WDW-2型微机电子万能试验机进行准静压力学特性试验,测得4个含水率下的蓖麻蒴果在顶部加载及中部加载下的破壳力,并根据试验结果将破壳过程分为达到破壳力、外种皮破裂及籽粒破损三个阶段。试验结果表明:品种对球度无显著影响;品种对破壳力有显著影响,1987品种蒴果破壳力最小,通蓖7号及通蓖11号次之,通蓖9号最大;含水率对破壳力有极显著影响,破壳力与含水率呈二次曲线关系;加载方式对破壳力有显著影响。其次将蓖麻蒴果视为球体,计算其在51.26N的作用下球心应力为0.80MPa。最后以通蓖11号蒴果为例,对破壳各阶段进行有限元分析。结果表明:顶部加载下达到破壳力时室与室结合破坏,在内侧形成缺口,外种皮破裂时裂纹在缺口处延伸,单室蒴果在法向最大轴线处种皮破裂,籽粒破损时籽粒裂纹在法向最大轴线处形成;中部加载下达到破壳力时,外种皮破裂阶段与顶部加载相同,籽粒破损阶段裂纹出现在切向最大轴线处。仿真分析得到的裂纹与试验结果一致,中心点处应力计算值与仿真结果比值为1.17。研究结果可为蓖麻蒴果脱壳机关键部件的设计提供参考。

In order to explore the changing rule of breaking force and breaking mechanism of castor shelling,the varieties of Variety 1987,Tongbi 7,9 and 11 were taken as the research object in this article.The sphericity of castor fruit was calculated firstly,and the quasi-static pressure characteristics to measure the shell breaking force at the top and middle loading of the castor fruit at 4 moisture contents was measured by WDW-2 microcomputer electronic universal testing machine.According to the experimental result,the broken process was divided into three stages:the breaking force,the exocarp rupture and the grain damage.The result showed that the variety has no significant effect on sphericity,but it has a significant effect on the breaking force.The lowest breaking force was Variety 1987,followed by Tongbi 7 and Tongbi 11,and Tongbi 9 was the largest one.The moisture content had a very significant effect on the breaking force.It was quadratic curve relationship between the breaking force and the moisture content.The loading method had a significant effect on the breaking force.Next,the castor fruit was regarded as a sphere,and its center stress under the force of 51.26N was calculated to be 0.80MPa.Finally,using Tongbi 11 as the mechanical model,finite element analysis was performed on various stages of shell breaking.The results showed that the chamber-to-chamber combination was broken when the top-loading reached the breaking force.The notch was formed at the inside and extend at the gap where is the maximum axis of normal in single chamber capsule when the exocarp rupture,and the seed cracks formed at the maximum axis of the normal direction when the grain was damaged.Under the middle loading,the breaking force and the exocarp rupture had the same phenomenon as the top loading,but the seed crack appeared at the maximum tangential axis when the grain was damaged.The crack obtained by simulation analysis was consistent with the test result,and the ratio of stress calculation value at the center point to simulation result was 1.17.The study may provide reference for research on the design of the key parts of the castor shelling machine.